If you're having issues achieving a proper fit with your in-ear headphones, below are some alternative options to explore.
Comply offers foam ear tips that will fit our in-ear headphones, with the exception of the T5 True Wireless which have a different type or ear tip connection. They make a few different styles and each has a small medium and large size to choose from.
Sport Pro Sx-100 http://www.complyfoam.com/products/s-100/
Isolation T-100 http://www.complyfoam.com/products/t-100/
Comfort Ts-100 http://www.complyfoam.com/products/ts-100/
Variety Pack 100 http://www.complyfoam.com/products/v-variety-pack-100/
Dekoni Audio sells their Gemini 3mm ear tips through the following dealer websites.